1. Field of the Invention
This invention relates to novel liquid crystalline compounds and liquid crystalline mixtures containing the same, and more particularly, it relates to chiral smectic compounds which have a high response rate and are superior as a ferroelectric liquid crystalline material, and also to chiral smectic mixtures containing the same.
2. Description of the Prior Art
Twisted nematic (TN) type display mode has currently been most widely employed as liquid crystal display elements, but it is inferior in the response rate as compared with emissive type display elements such as electroluminescence, plasma display, etc., and various attempts for overcoming this drawback have been made, but, nevertheless, it seems that its improvement to a large extent has not been left behind. Thus, various liquid crystal display equipments based on different principles in place of TN type display elements have been attempted, and as one of them, there is a display mode utilizing ferroelectric liquid crystals (N. A. Clark and S. T. Layerwall, Applied Phys. lett., 36,899 (1980)). This mode utilizes the chiral smectic C phase (hereinafter abbreviated to SC* phase) or chiral smectic H phase (hereinafter abbreviated to SH* phase) of ferroelectric liquid crystals. As such ferroelectric liquid crystal compounds, the following compounds (1) to (4) have been known up to the present (ph. Martino Lagarde, J. de Physique, 37, C3-129 (1976)): ##STR3##
In the foregoing, C represents crystalline phase; SA, smectic A phase; I, isotropic liquid phase; SC* and SH*, as described above; and "*", asymmetric carbon atom.
Further, as ferroelectric liquid crystal compounds, the following two compounds (5) and (6) have also been known: ##STR4##
(B. I. Ostrovski, A. Z. Rabinovich, A. S. Sonin, E. L. Sorkin, B. A. Strukov, and S. T. Taraskin; Ferroelectrics, 24, 309 (1980)).
Among these compounds, since the compounds (1) to (4) have C.dbd.C double bond and azomethine group, they have drawbacks of being inferior in light reistance and water resistance. The compounds (5) also have azomethine group and hence are inferior in water resistance. The compounds (6) do not have these bonds and hence are superior in stability, but the above Ostrovski et al's article discloses as to their phase transition temperatures, only that the upper limit temperatures of SC* phase are 324.8.degree. K. (in the case of n=9) and 326.2.degree. K. (in the case of n=10), but nothing is disclosed therein as to other liquid crystalline phase modifications.
The present inventors have investigated and studied various compounds including the above compounds (1) to (6) and as a result, have found ferroelectric liquid crystal compounds having a superior stability.
A group of these compounds is those previsouly filed as U.S. Ser. No. 568,060 (Jan. 4, 1984) now U.S. Pat. No. 4,596,667, and expressed by the following general formula: ##STR5## wherein ##STR6## represents 1,4-phenylene group ##STR7## or 1,4-trans-cyclohexane group ##STR8## R*, an optically active alkyl group; m=0, 1 or 2; n=1 or 2; X, a linear chain or brached alkyl group or alkoxy group, each having 1 to 18 carbon atoms; and when ##STR9## represents ##STR10## m=1; and n=1, X represents a linear chain or branched alkyl group having 1 to 18 carbon atoms or a linear chain alkoxy group having 11 to 18 carbon atoms.
The compounds of the present invention are also used for the same object as that of the above compounds.